Cattle tracking has traditionally been done by tagging cattle with a visual indicator showing a number. This visual indicator was previously done by branding but is more commonly done now with ear tags. Visual indicators require substantial time and effort on the part of owners to track large number of cattle.
In the past decade, passive Radio Frequency Identification (RFID) began to be used in tagging cattle. Passive RFID involves sending small amounts of energy and signals to a device in close proximity to the transmitter. The transmitted energy provides enough power for the RFID tag to process information and to send back a signal to the transmitter, thus providing an identification of the device that contains the RFID tag. The use of RFID in cattle tracking requires that the cattle come very close to (within a few meters of) the transmitter. Passive RFID tags are only powered when in close proximity to the transmitter (which occurs only a small fraction of each day), so these tags are unable to collect any information about the animal.
Active RFID tags must be powered by a power source such as a battery. Active RFID tags are capable of collecting information and relaying that information back to the transmitter. However, the drain on the battery presents problems with need to frequently replace the batteries in the field. Furthermore, the power level achieved by a small battery inside an ear tag would be inadequate to transmit standard RF signals over any appreciable distance. Thus, active RFID tags suffer from the same deficiencies as passive RFID tags, except that they are capable of collecting information about the animal even when not in range of the transmitter.